The present invention relates to a polyvinyl chloride resin-based composition having good workability and capable of giving a shaped article with excellent impact strength.
With an object to improve the impact strength of a shaped article obtained from a polyvinyl chloride resin, attempts have been made heretofore to admix a polyvinyl chloride resin with an impact strength improver which is a copolymeric resin of acrylonitrile, butadiene and styrene, referred to as an ABS resin hereinbelow, a copolymeric resin of methyl methacrylate, butadiene and styrene, referred to as an MBS resin hereinbelow, a copolymeric resin of ethylene and vinyl acetate, referred to as an EVA resin hereinbelow, a styrene-butadiene copolymeric rubber, referred to as an SBR hereinbelow, or the like.
One of the problems in the use of an ABS resin, MBS resin or SBR as the impact strength improver is that the shaped article obtained from such a polyvinyl chloride resin composition has relatively low weatherability because these polymers contain double bonds in the molecular structure thereof having susceptibility to the influence of visible and ultraviolet lights and heat. Addition of an antioxidant, ultraviolet absorber and the like to such a polyvinyl chloride resin composition can be a remedy for this defect but this measure can never give a quite satisfactory result in respect of the properties of the shaped articles of the resin composition.
On the other hand, EVA resins as an impact strength improver have another problem that delicate adjustment is required in the molding conditions such as the molding temperature because the polyvinyl chloride resin and the EVA resin may be uniformly melted together resulting in a decrease in the impact strength of the shaped articles when the molding temperature is too high or the staying time of the resin composition in the molding machine is too long.
Further, it is a usual formulation that a polyvinyl chloride resin composition is compounded with a large amount of an inorganic filler with an object to impart the shaped article obtained from the resin composition with improved flame retardancy. When the amount of the compounded inorganic filler is increased, a decrease is caused in various properties of the shaped articles of the resin composition such as impact strength, tensile strength and the like. In addition, most of these fillers consist of finely divided particles having a low coefficient of friction between particles so that compounding of a polyvinyl chloride resin composition with such an inorganic filler has an effect that, when the resin composition is molded by extrusion molding using an extruder machine, the rate of extrusion is decreased at a specified temperature and under a specified pressure to increase the staying time of the resin composition in the extruder machine adversely influencing on the quality of the shaped articles in addition to the problems of scorch, plate-out and the like.